export default {
  mounted(el, binding) { // el为绑定的元素，binding为绑定给指令的对象
      let width = '', height = '';
      function isReize() {
        const style = document.defaultView.getComputedStyle(el);
        if (width !== style.width || height !== style.height) {
          binding.value();  // 关键
        }
        width = style.width;
        height = style.height;
      }
      el.__vueSetInterval__ = setInterval(isReize, 300);
    },
    unmounted(el) {
      clearInterval(el.__vueSetInterval__);
    }
}